The term "paint" as hereafter applied refers to coatings such as enamel, latex, lacquer, varnish, shellac and polyurethane finishes used to protect and/or beautify substrates. If applied by wiping, a paint remover can also serve to "degloss" an applied finish so that it will be suitably prepared for application of a new coat of paint. When used on brushes or other coatings applicators, some paint removers can also remove hardened paint from the brush or applicator thereby restoring it to useable condition. As used herein, the term "paint remover" refers to compositions which can strip or facilitate the stripping of "paint" from a substrate to which it is applied.
Chemical paint removers have achieved considerable popularity because they are much easier to use than the non-chemical alternatives, such as blow torches and power sanders. These chemical paint removers fall into two basic categories. One category is a caustic-based remover which is seldom used in home applications because it requires heating and the use of dip tanks. These caustic based removers also have a deleterious effect on many kinds of wood, and often dissolve the glue holding the furniture together.
The second category of paint removers, which also is the more popular type, contains an organic chemical solvent base. A typical composition of such a paint remover is disclosed in U.S. Pat. No. 2,507,983. This patent discloses a paint remover containing methylene chloride (85% by weight of the mixture) as the active compound with methanol and methycellulose being added as a thickener. Paint removers such as these containing methylene chloride are generally very effective in removing varnish and alkyd paint. They are less effective on lacquer and latex finishes. Unthickened removers which have high concentrations of methanol and benzene are often used for varnish removal.
However, most known varnish and paint removers suffer from serious performance defects. They evaporate so rapidly that the surface tends to dry out before the finish is sufficiently softened to allow for its easy removal. Methylene chloride, for example, has a vapor pressure so high (400 mm Hg at 75.degree. F.) that it evaporates very rapidly. Typically, as mentioned in U.S. Pat. No. 2,507,983, wax is added to form a vapor barrier to retard its evaporation. However, after such waxy compositions are applied, cross brushing of the paint remover or testing of the surface must be avoided or the barrier film will crack and permit the solvent to evaporate and escape. The wax itself is also regarded as a serious handicap by furniture refinishers because it must be removed completely before applying the new finish.
The most serious objection to these prior art paint removers is their high degree of toxicity. (See for examples Consumer Reports, March, 1972, p. 147.)
A thorough literature study on methylene chloride toxicity in particular confirms that it is extremely hazardous. The primary avenue of contact is by vapor inhalation, due in large measure to its very high vapor pressure. It has been shown that even with moderate ventilation, methylene chloride levels can rise to 1200 ppm in the breathing zone of a person using this material to strip paint. With less ventilation, as is commonly encountered in home use, levels rise much higher. In addition, methylene chloride is metabolized to carbon monoxide, the presence of which places stress on the cardiovascular system and can cause heart attacks and death. Literature dealing with this subject includes Richard D. Stewart, et al, The Journal of the American Medical Association, Volume 235 (4), Page 398, Jan. 26, 1976, and R. S. Ratney, et al, Archives of Environmental Health, Volume 28 (8), Pages 223-6, 1974.
Prolonged exposure to methylene chloride also depresses the activity of the nervous system, decreasing alertness and disturbing sleep patterns. (G. G. Fodor, and H. Winneke, Proceedings International Clean Air Congress, 2nd, 238-43, 1970.) The body's ability to respond to stress therefore is decreased, thereby compounding the problem associated with metabolism of the methylene chloride to carbon monoxide. Repeated exposure to methylene chloride has also been shown to result in digestive disorders and liver damage. (C. C. Haun, et al, U.S. National Technical Information Service, AD Report, 1971 #751432).
Another objection to paint removers containing methylene chloride is that they can burn the skin, producing varying degrees of dermatitis depending upon the duration of contact with the skin.
Methanol is also commonly used in paint strippers. If used with methylene chloride as it often is, it prolongs the period of cardiovascular stress caused by the methylene chloride. Furthermore, it is also toxic in its own right. According to N. Irving Sax, Dangerous Properties of Industrial Materials, Van Nostrand Co., NY, 1968, at page 911, methanol should be regarded as a cumulative poison because of the slowness with which it is eliminated from the human body. Severe exposure to methanol is said to cause dizziness, unconsciousness, irregular respiration, cardiac depression and eventually death. Where the exposure is less severe, the first symptoms may be blurring of vision, photophobia and conjunctivitis, followed by the development of definite eye lesions. Headache, gastrointestinal disturbances, dizziness, and a feeling of intoxication may also be experienced. The visual symptoms may clear temporarily, only to recur later and progress to blindness.
Another constituent of many paint removers is benzene. Its toxicity is only moderate for a single exposure. However, it induces severe chronic toxic effects, causing anemia and damage to the bone marrow. Ultimately, it can cause death.
Acetone is among numerous other chemicals which have been used in chemical paint removers. Acetone has low toxicity but has such a high vapor pressure that it, like methylene chloride, does not stay on the surface long enough to cut through multiple layers of paint. It also presents a fire hazard. It is therefore not suitable as a basis for a paint removing composition.
Other types of paint removers have been suggested. For example. U.S. Pat. No. 3,702,304 discloses use of oil-in-water emulsions containing xylene and either dimethyl formamide, dimethyl acetamide, or dichloromethane. U.S. Pat. No. 3,355,385 shows a number of mixtures which all contain hydrogen peroxide. Hydrogen peroxide is a powerful oxidizing agent which is therefore too hazardous for common household use because it attacks the skin and eyes. Phenol and cresols also are also mentioned, but these are too toxic for safe use in non-industrial paint removers. Likewise suffering from the disadvantage of high toxicity is a paint remover containing methylene chloride and n-methyl 2-pyrrolidone, suggested in Methyl Pyrrolidone, Antara Chemicals (Division of GAF Corporation), 1961, pages 24-26.
M-Pyrol Handbook, GAF Corporation, 1972, page 52, suggests a paint remover consisting of thickened N-methyl 2-pyrrolidone (hereinafter referred to as "NMP"). Currently, NMP costs over four times as much as methylene chloride and ten times as much as other common paint remover constituents. The high cost of NMP significantly increases the cost of the paint remover.
U.S. Pat. No. 4,120,810 relates to mixtures of NMP and blends of alkyl naphthalenes and alkyl benzenes having molar volumes greater than or equal to about 140 cc/g. Mixtures of this type are alleged to exhibit paint removal properties equal to NMP itself while having reduced cost. However, due to the cost of NMP, these mixtures still presently cost far more than paint stripping compositions currently in widespread commercial use. While alternate technologies have been proposed, none promise to significantly reduce the cost of production of NMP, and make it cost competitive with methylene chloride.
Accordingly, an object of this invention is to provide improved paint removers which have reduced toxicity.
Another object is to provide an improved paint remover which does not burn the skin and which has reduced volatility.
A further object is an improved paint remover that is safe, effective, and of a reasonable cost.